The present invention relates to a unit, and to a relative method, for wrapping tobacco products.
Wrapping units of the type referred to herein can be utilized in packer machines by which groups of cigarettes, each enveloped previously in an inner wrapper of metal foil paper, are enfolded in packets of soft type.
Another application for such units, for example, is that of machines by which packets of cigarettes are overwrapped, also known as cellophaners.
The wrapping material used by a cigarette packer consists in leaves of a pliable paper, whereas the material used by a cellophaner consists in leaves of a transparent thermoplastic film.
The tobacco products, whether groups of cigarettes or completed packets, will generally present the appearance of a rectangular prism delimited axially by two end faces, and transversely by two larger lateral faces and two smaller lateral faces, or flank faces, extending parallel to a longitudinal axis.
The products are wrapped by a unit of the type in question while advancing along a predetermined feed direction.
To obtain a correctly formed wrap, given the high output speeds at which modern packaging machines are designed to operate, it is indispensable that the leaves of wrapping material be kept continuously and fully under control when fed to the unit and during the wrapping steps, to ensure that they do not become incorrectly positioned and mis-timed relative to the products, as this would result in the finished packet wrapper or overwrap presenting unsightly creases or blemishes.
Wrapping units of conventional type comprise a transfer system by which the aforementioned tobacco products are directed along a predetermined path and through an assembly station where each one is paired with a leaf of wrapping material, consisting of paper in the case of a cigarette packer, and polypropylene in the case of an overwrapper.
The leaf is separated from a continuous strip of wrapping material by a cutting step and fed to the assembly station through the agency of a conveyor that comprises a vacuum roller, set in continuous rotation.
The product transfer system comprises a wrapping wheel set in rotation continuously about an axis parallel to the axis of the vacuum roller, and revolving tangentially to the selfsame roller at the assembly station.
The wrapping wheel is furnished peripherally with a plurality of mechanisms rotatable about corresponding pivots parallel to the axis of the wrapping wheel, each supporting a respective product.
Each of the support mechanisms incorporates a gripper by which one end of a respective leaf of wrapping material, advancing on the vacuum roller, is intercepted at the assembly station.
The transfer of the leaf of material to the mechanism holding a relative product occurs with the jaws of the gripper spread apart in readiness to receive, and is favored by a higher tangential velocity of the vacuum roller.
At the moment when the end or leading edge of the leaf registers in contact with the bottom of the slot afforded by the open gripper, the jaws close and the support mechanism begins to turn on the respective pivot, whereupon the leaf of material will be bent, with the aid also of fixed folding means, and formed gradually into a tubular wrap around the product.
While effective, this conventional wrapping method has been found nonetheless to occasion certain drawbacks, particularly when operating at the high output speeds of modern packaging machines.
It happens frequently that the jaws of the gripper do not close exactly at the moment when the leaf makes contact.
The closing movement of the gripper jaws may be retarded or advanced, but in either case the position assumed by the leaf of wrapping material in relation to the corresponding product will be incorrect, and the wrap consequently defective. Where the closing movement is retarded, moreover, the leaf will be deformed on striking the gripper, and pinched against the bottom of the slot between the jaws.
The object of the present invention is to provide a unit for wrapping tobacco products such as will be able to meet the operating requirements implicit in the foregoing outline, with regard to the high output speeds of modern cigarette packers and cellophaners.
A further object of the invention is to provide a method of wrapping tobacco products such as will be able to meet the operating requirements implicit in the foregoing outline, with regard likewise to the high output speeds of modern machines.